1. Field of the Invention
The present invention relates generally to a method of quantifying the coverage of extra particulate additives (EPA) on the surface of toner particles. More specifically, this invention is a method using automated image analysis to correctly identify toner and coverage of EPA particles on the surface of the toner.
2. Description of the Related Art
Toner may be utilized in image forming devices, such as printers, copiers and/or fax machines, to form images on a sheet of media. The image forming apparatus may transfer the toner from a reservoir to the media via a developer system utilizing differential charges generated between the toner particles and the various components in the developer system. Electrophotographic printing may be carried out using a monocomponent development (MCD) system that requires the use of a toner adder roll, developer roll, and doctor blade for charging and doctoring the toner, or a dual component development (DCD) system which requires the use of a magnetic carrier and a magnetic roll to help charge the toner. Using a DCD system has the advantage of using fewer components and possibly allowing for longer life cartridges and hence, a lower cost per page. Regardless of whether the toner is charged via MCD or DCD process, printing uses the same process of toner transfer to an imaging substrate that has been discharged via light, such as a photoconductor or photoreceptor drum or belt. Toner is then directly transferred to a media sheet or to an intermediate image transfer member before being transferred onto a media sheet.
Toner particles consist of resin, wax, pigments, and other components. Toner particles used in the printing process are typically treated with surface additives. The particles are covered with extra particulate additives (EPA) to provide the correct triboelectric and rheology characteristics. These EPAs are based on silicon dioxide also known as silica, titanium dioxide also known as titania, aluminum oxide also known as alumina, and/or composite mixtures of titania, silica, and/or alumina.
The effectiveness of toner particles depend on having an adequate coverage on each toner particle. If the toner particles contain too much or too little coverage of EPA particles on the surface, the print quality will be negatively impacted. Additionally, the printer will consume too much toner per printed page. The same would be true if some EPAs end up embedded into the surface of a toner particle. A small change of EPA coverage on the toner particles is significant for performance but cannot be easily quantified by simple visual inspection, even using such methods as scanning electron microscopy (SEM).
Previous methods to determine EPA coverage of the toner surface, such as X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), and inductively couple plasma (ICP) analyses involved bulk measurements and were incapable of discerning embedded and/or knocked off EPA particles. There is therefore a need for a method to quantitatively determine the EPA coverage of the toner surface that can provide reproducibility and precision that is beyond the capabilities of the human eye.